Change: Improve error message if model can't be created

Sometimes the models are incomplete or the schema description at the
GitHub REST API docs are wrong, in this case we need error information
about which property can't be set from which value. This allows for
easier fixing of the model.

pontos/models/__init__.py

@@ -22,6 +22,8 @@
 
 from dateutil import parser as dateparser
 
+from pontos.errors import PontosError
+
 try:
     from typing import get_args, get_origin
 except ImportError:
@@ -30,6 +32,12 @@
 __all__ = ("Model",)
 
 
+class ModelError(PontosError):
+    """
+    Errors raised for Models
+    """
+
+
 def dotted_attributes(obj: Any, data: Dict[str, Any]) -> Any:
     """
     Set dotted attributes on an object
@@ -147,12 +155,18 @@ def from_dict(cls, data: Dict[str, Any]):
         additional_attrs = {}
         type_hints = get_type_hints(cls)
         for name, value in data.items():
-            if isinstance(value, list):
-                model_field_cls = type_hints.get(name)
-                value = [cls._get_value(model_field_cls, v) for v in value]
-            elif value is not None:
-                model_field_cls = type_hints.get(name)
-                value = cls._get_value(model_field_cls, value)
+            try:
+                if isinstance(value, list):
+                    model_field_cls = type_hints.get(name)
+                    value = [cls._get_value(model_field_cls, v) for v in value]
+                elif value is not None:
+                    model_field_cls = type_hints.get(name)
+                    value = cls._get_value(model_field_cls, value)
+            except TypeError as e:
+                raise ModelError(
+                    f"Error while creating {cls.__name__}. Could not set value "
+                    f"for '{name}' from '{value}'."
+                ) from e
 
             if name in type_hints:
                 kwargs[name] = value

tests/models/test_models.py

@@ -22,7 +22,7 @@
 from datetime import date, datetime, timedelta, timezone
 from typing import Dict, List, Optional, Union
 
-from pontos.models import Model, ModelAttribute, dotted_attributes
+from pontos.models import Model, ModelAttribute, ModelError, dotted_attributes
 
 
 class ModelTestCase(unittest.TestCase):
@@ -197,3 +197,15 @@ class ExampleModel(Model):
 
         model = ExampleModel.from_dict({"foo": [{"a": 1}, {"b": 2}, {"c": 3}]})
         self.assertEqual(model.foo, [{"a": 1}, {"b": 2}, {"c": 3}])
+
+    def test_model_error(self):
+        @dataclass
+        class ExampleModel(Model):
+            foo: Optional[str] = None
+
+        with self.assertRaisesRegex(
+            ModelError,
+            "Error while creating ExampleModel. Could not set value for 'foo' "
+            "from '{'bar': 'baz'}'.",
+        ):
+            ExampleModel.from_dict({"foo": {"bar": "baz"}})